Key Points:

  • Heavy rain and strong winds have begun to lash the Bay of Plenty
  • The region could see 110mm of rain over 12 hours, with the worst rain east of Opotiki
  • Trees are down, trampolines are flying and power has been cut to a swathe of Rotorua
  • Winds up to 100km/hr expected tonight in Auckland

Heavy rain has lashed the already-sodden Bay of Plenty, with the region braced for up to 110mm in the space of 12 hours overnight.

Large trees have come down and power has been cut to suburbs in Rotorua and Tauranga, which have been battered by heavy rain and high winds.

Rotorua Daily Post Facebook readers have reported trampolines flying away in the high winds and there have been reports of water on some roads in the district.

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About 1000 homes are without power in the western Bay of Plenty, including 600 in the Tauranga suburb of Pyes Pa. More than a dozen outages are affecting residents in the Far North and Bay of Islands, while 250 homes have no power in Inglewood in Taranaki.

In Auckland, Vector has restored power in St Heliers and Waiheke, and is responding to outages in Whitford, Helensville and South Head.

One-hundred-and-fifty Taihape homes are still without power after last week's storm. Power was earlier cut to more than 900 homes and businesses in the district, mostly near Lake Okareka, although it has since been restored.

Warnings have been issued across the country as the school holidays end with a storm that threatens to wreak widespread havoc.

"This is a significant weather event and the combination of heavy rain and strong winds is expected to cause widespread disruption to transport, localised flooding and slips," MetService said.

"Winds of this strength can cause damage to trees, powerlines, unsecured roofs and structures, and make driving hazardous. Also in the South Island, wind chill due to cold temperatures and strong winds could cause stress to livestock."

Alerts have been issued by Civil Defence to prepare for flooding, with the heaviest downpours expected to fall east of Opotiki.

"Beware of hazardous driving conditions, with slips and surface flooding possible," Bay of Plenty Civil Defence said on their Facebook page.

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"For those of you just getting into calving, remember the ground is already quite wet, take care in the paddocks and make sure you have a mate who can tow you out."

At its peak, rain could intensify to 20mm to 30mm per hour.

Northeast gales are expected to become severe this afternoon, gusting 120km/h in exposed places, easing overnight tonight.

In Auckland, northeast gales are also expected to become severe this afternoon, gusting 100km/h in exposed places.

That could mean chaos on the motorways for city commuters.

The gales are expected to ease overnight.

"Everyone really needs to take a raincoat in the North Island but it's really that Bay of Plenty where the heavy rain targets tonight," said Metservice forcaster Georgina Griffiths.

Wellingtonians will probably breathe a sigh of relief with only "ordinary bad weather", she said.

A slip earlier this week closed State Highway 4 - the Whanganui to Raetihi route - north of Fields Track at the Hapokopoko Bluffs.

NZTA's regional transport system manager Ross I'Anson said the road is expected to be closed until late tomorrow. The slip dumped about 500 cubic metres of material onto the road.

Tomorrow is expected to usher in the worst of the winter storm as it stalls over Canterbury and Otago bringing snow down to 400m.

"It's really the eastern South Island that sees the worst of this, heavy rain warnings - and they're quite large ones - between Dunedin and Canterbury," Griffiths said.

"That will probably cause impact ... we possibly will see flooding in those regions."

As well as snow, parts of Canterbury are expecting more than a month's worth of rain in a day.

MetService said the heaviest falls were expected in Canterbury and eastern Otago, including Dunedin, where up to 160mm of rain was expected to fall tomorrow.

The predicted rainfall was similar to that forecast just before Easter, but over a shorter period, said Otago District Council director environmental monitoring and operations, Scott MacLean.

Based on the current forecast, the Kakanui, Shag, Kauru and Waianakarua Rivers in North Otago and the Leith, Silver Stream and Taieri Rivers are all expected to rise swiftly.

"We'd ask people to be aware that with such heavy rainfall, we expect surface flooding to affect roads and low-lying properties," MacLean said.

"We will be issuing updates regularly on the Otago Regional Council's website, Facebook and Twitter accounts and via the media. People can also see river levels and rainfall for themselves on our WaterInfo page, www.orc.govt.nz/waterinfo .

As well as monitoring river levels, the ORC's staff are out visiting pump stations to check that they are operating as expected.

Emergency Management Otago is also monitoring the situation. Regional Manager Chris Hawker said his staff would be ready to activate in support of Dunedin City and Waitaki District Councils if required.

The Christchurch Traffic Centre is telling motorists to allow an extra 45 minutes for travel if travelling between Christchurch and Picton.

"Snow and ice are possible again on the major South Alpine mountain passes, so motorists need to ensure that their vehicles are well maintained and to drive to the conditions," they said in a statement.

What's happening in your area

Auckland and Great Barrier Island

Northeast gales are expected to become severe this afternoon, gusting 100km/h, then ease this evening.

Bay of Plenty and Rotorua

Rain is expected to become heavy this afternoon, and ease overnight tonight.

In the 12 hours from 2pm this afternoon to 2am Friday morning, expect 90 to 100mm of rain. Peak intensities of 20 to 30mm per hour.

Northeast gales are expected to become severe this afternoon, gusting 120km/h in exposed places, easing overnight tonight.

Canterbury north of the Rakaia River

Rain is expected to become heavy on Friday morning and ease overnight Friday.

In the 20-hour period from 6am Friday to 2am Saturday, expect 120 to 160mm of rain about the foothills and ranges and 80 to 100mm towards the coast.

Peak intensities of 15mm to 20mm per hour. However, above 800m rain turns to snow from Friday evening.

Canterbury south of the Rakaia River and North Otago

Rain is expected to become heavy Friday morning and ease during Saturday morning.

In the 25-hour period from 7am Friday to 8am Saturday, expect 150 to 200mm of rain to accumulate. Peak intensities of 15 to 20mm per hour.

Dunedin

Rain is expected to become heavy around midday Friday and ease early Saturday morning.

In the 18-hour period from midday Friday to 6am Saturday, expect 150 to 200mm of rain to accumulate. Peak intensities of 15 to 20mm per hour.